Chronic back problems can cause pain and disability for a large segment of the population. Frequently, the cause of back pain is traceable to diseased disk material between opposing vertebrae. When the disk material is diseased, the opposing vertebrae may be inadequately supported, resulting in persistent pain.
Surgical techniques have been developed to remove the diseased disk material and fuse the joint between opposing vertebral bodies. Arthrodesis of the intervertebral joint can reduce the pain associated with movement of an intervertebral joint having diseased disk material. Generally, fusion techniques involve removal of the diseased disk, drilling a bore for receiving the implant and inserting the implant between the opposing vertebral bodies.
Spinal fusion implants and related surgical instruments for implanting a fusion device are known and disclosed in, for example, U.S. Pat. Nos. 5,741,253; 5,658,337; 5,609,636; 5,505,732; 5,489,308; 5,489,307; 5,484,437; 5,458,638; 5,055,104; 5,026,373; 5,015,247; and 4,961,740.
Procedures for fusing an intervertebral joint space typically include placement of at least two cylindrical implants in parallel arrangement between the opposing vertebrae. Recently, non-circular implants have been introduced that provide for placing parallel implants in close proximity to one another. Examples of such implants are disclosed in, for example, U.S. Pat. Nos. 5,658,337; 5,593,409; and 5,489,307, the entire disclosures of which are incorporated herein by reference. These non-circular implants may be referred to as reduced lateral profile (RLP) implants and typically have a side wall geometry that permits placement of two RLP implants or one RLP and one cylindrical implant in closer proximity to one another. Thus, greater surface area support of the intervertebral space and/or increased distraction of the disk space can be provided for a given medial/lateral dimension of the vertebral body.
Some presently available systems for implanting fusion devices permit for preparing an implant site through a hollow tube. Procedures for preparing an implant site through a single hollow tube are shown in, for example, U.S. Pat. Nos. 5,505,732; 5,484,437; and 5,489,307. The disclosure of each of these patents are incorporated herein by reference. In some procedures, the implants are also inserted into the prepared site through the hollow tube. Preparing the implant site by passing instruments through a hollow tube advantageously provides for an isolated surgical field with reduced chance of injury to soft tissues surrounding the surgical site.
However, generally, several steps are required for appropriate placement of the implants using present hollow tube systems. These steps include inserting a spacer into the disk space to distract one side of the intervertebral space, then inserting a second spacer for distracting the second side of the vertebral space, followed by placement of the hollow tube over a guiding mechanism to orient the longitudinal angulation of the implant site. Once the hollow tube is secured in proper alignment, reamers, bores, taps, or other instruments are passed through the hollow tube to prepare the implant site. Either before or after the implant is inserted into the first site, the hollow tube is removed and the procedure is repeated on the opposite side.
Present procedures for placement of an implant through a hollow tube help to reduce the chance of iatrogenic tissue trauma caused by the implant procedure. However, while known procedures provide for reduced chance of injury, the surgeon's accuracy in the relative placement of the hollow tube between the first and second sides is still a matter of guess work and repeated verification using fluoroscopy or radiographic monitoring is needed. Also, the need for separate placement of the hollow guide tube using present methods (i.e., one placement for each implant) increases the possibility for relative misalignment of the implants to occur during insertion.
Thus, there is a continuing need for the precision, safety and ease of placement of spinal fusion implants. There is also a need for implant insertion systems that accommodate implants having non-circular cross-sectional geometries. The present invention is directed to addressing these needs.